package neolith;

/**
 *  字符串相关工具类
 */
public class StringUtils {

  private StringUtils() {
    throw new UnsupportedOperationException("u can't instantiate me...");
  }

  /**
   * 判断字符串是否为null或长度为0
   *
   * @param s 待校验字符串
   * @return {@code true}: 空<br> {@code false}: 不为空
   */
  public static boolean isEmpty(CharSequence s) {
    return s == null || s.length() == 0;
  }

  /**
   * 判断字符串是否为null或全为空格
   *
   * @param s 待校验字符串
   * @return {@code true}: null或全空格<br> {@code false}: 不为null且不全空格
   */
  public static boolean isSpace(String s) {
    return (s == null || s.trim().length() == 0);
  }

  /**
   * 判断两字符串是否相等
   *
   * @param a 待校验字符串a
   * @param b 待校验字符串b
   * @return {@code true}: 相等<br>{@code false}: 不相等
   */
  public static boolean equals(CharSequence a, CharSequence b) {
    if (a == b) return true;
    int length;
    if (a != null && b != null && (length = a.length()) == b.length()) {
      if (a instanceof String && b instanceof String) {
        return a.equals(b);
      } else {
        for (int i = 0; i < length; i++) {
          if (a.charAt(i) != b.charAt(i)) return false;
        }
        return true;
      }
    }
    return false;
  }

  /**
   * 判断两字符串忽略大小写是否相等
   *
   * @param a 待校验字符串a
   * @param b 待校验字符串b
   * @return {@code true}: 相等<br>{@code false}: 不相等
   */
  public static boolean equalsIgnoreCase(String a, String b) {
    return (a == b) || (b != null) && (a.length() == b.length()) && a.regionMatches(true, 0, b, 0, b.length());
  }

  /**
   * null转为长度为0的字符串
   *
   * @param s 待转字符串
   * @return s为null转为长度为0字符串，否则不改变
   */
  public static String null2Length0(String s) {
    return s == null ? "" : s;
  }

  /**
   * 返回字符串长度
   *
   * @param s 字符串
   * @return null返回0，其他返回自身长度
   */
  public static int length(CharSequence s) {
    return s == null ? 0 : s.length();
  }

  /**
   * 首字母大写
   *
   * @param s 待转字符串
   * @return 首字母大写字符串
   */
  public static String upperFirstLetter(String s) {
    if (isEmpty(s) || !Character.isLowerCase(s.charAt(0))) return s;
    return (char) (s.charAt(0) - 32) + s.substring(1);
  }

  /**
   * 首字母小写
   *
   * @param s 待转字符串
   * @return 首字母小写字符串
   */
  public static String lowerFirstLetter(String s) {
    if (isEmpty(s) || !Character.isUpperCase(s.charAt(0))) return s;
    return (char) (s.charAt(0) + 32) + s.substring(1);
  }

  /**
   * 反转字符串
   *
   * @param s 待反转字符串
   * @return 反转字符串
   */
  public static String reverse(String s) {
    int len = length(s);
    if (len <= 1) return s;
    int mid = len >> 1;
    char[] chars = s.toCharArray();
    char c;
    for (int i = 0; i < mid; ++i) {
      c = chars[i];
      chars[i] = chars[len - i - 1];
      chars[len - i - 1] = c;
    }
    return new String(chars);
  }

  /**
   * 转化为半角字符
   *
   * @param s 待转字符串
   * @return 半角字符串
   */
  public static String toDBC(String s) {
    if (isEmpty(s)) return s;
    char[] chars = s.toCharArray();
    for (int i = 0, len = chars.length; i < len; i++) {
      if (chars[i] == 12288) {
        chars[i] = ' ';
      } else if (65281 <= chars[i] && chars[i] <= 65374) {
        chars[i] = (char) (chars[i] - 65248);
      } else {
        chars[i] = chars[i];
      }
    }
    return new String(chars);
  }

  /**
   * 转化为全角字符
   *
   * @param s 待转字符串
   * @return 全角字符串
   */
  public static String toSBC(String s) {
    if (isEmpty(s)) return s;
    char[] chars = s.toCharArray();
    for (int i = 0, len = chars.length; i < len; i++) {
      if (chars[i] == ' ') {
        chars[i] = (char) 12288;
      } else if (33 <= chars[i] && chars[i] <= 126) {
        chars[i] = (char) (chars[i] + 65248);
      } else {
        chars[i] = chars[i];
      }
    }
    return new String(chars);
  }
}
